Download Social Studies Summary earthquakes volcanoes

Social Studies :Grade 6
Unit two
Lesson 1 (Earthquakes)
The Earth consists of these layers : inner core, outer core, mantle and crust.
The lithosphere which consists of the crust and the upper mantle ,
is where the earth’s tectonic plates are found.
The lithosphere is the name of the place where an earthquake occurs on
the surface of the earth.
-The tectonic plates are constantly shifting , but when the plates move
against each other , they can build up tension and pressure, which
cause earthquakes .
-When the tectonic plates move against each other causing an
earthquake, they leave cracks on the earth’s surface which are called
faults.
A fault may move horizontally or vertically or both at the same time.
Epicenter is the point on the Earth's surface that is directly above the focus
(the point of origin) of an earthquake ,and underneath is called the
hypocenter.
When an earthquake happens, the energy released and radiates out from
where the earthquake originated .
*The ripples of energy are called seismic waves.
Scientists use an instrument called seismograph to measure
the size of the earthquake and how powerful it was.
Lesson 2 (Volcanoes)
A volcano is a vent in the Earth’s crust that releases some of the following
volcanic matter :lava ,ash, gases and pyroclastic flow.
*Types of volcanoes:
1-Shield Volcanoes: are the largest volcanoes in the world.
They are made up of basalt, a generally dark volcanic lava that is made up of silica and
rich in iron and magnesium.
Shield Volcanoes do not explode like Strato Volcanoes.
2-Strato Volcanoes: are the most common type of volcano on Earth.
They are made up of half lava and half pyroclastic material.
This combination creates a much more thick and sluggish lava than basalt.
It makes more gases causing the volcanic vents to get blocked ,which is why Strato
Volcanoes have more explosive eruptions than others.
These volcanoes are prone to mudslides , landslides and avalanches.
3-Cinder Cones: are uncommon and formed only by what is called a Strombolian
eruption.
* Types of Volcanic eruption:
1-An Icelandic eruption: is the least explosive volcanic eruption.
2-Hawaiian eruption : is very similar to Icelandic eruptions.
3-Strombolian eruptions: very little or no lava comes out of it.
4-Vulcanian eruptions: are bigger than Strombolian, these eruptions create
Strato volcanoes.
5-Pelean eruptions.
6-A Plinian eruptions.